This invention relates to a single-lens reflex camera having an automatic focus control device and a flash device, and more particularly to an auxiliary light emitting device for such a camera which, when an object to be photographed is low in brightness or in contrast, establishes an adequate focusing contrast for the object.
Recently, single-lens reflex cameras have been markedly automated, and a variety of such cameras with an automatic focus control and a built-in flash have been proposed.
The automatic focus control in many of these cameras employs systems which detect focusing condition of an objective lens based on the light which has passed through the objective lens. For example, when the object is dark or low in contrast, such as a white wall, the output is insufficient, and the lens cannot be accurately focused. In order to overcome this difficulty, an auxiliary light emitting unit for projecting a pattern of light and dark stripes towards the object has been employed. That is, when the object is dark or low in contrast, the striped pattern projecting unit is operated to project the striped pattern towards the object so that a contrast necessary for the focusing operation is obtained.
A single-lens reflex camera having the above-described function is shown in FIGS. 6 through 8, wherein FIG. 6 is a perspective view showing the essential components of a built-in flash unit, and FIGS. 7 and 8 are sectional diagrams taken along the optical axis of the camera showing the essential parts of a pop-up mechanism of the flash unit.
A penta housing 12 is mounted on the camera body 10, and a penta prism 14 is disposed in the housing. A chamber 16 for accommodating a flash unit casing 20 is provided in front of the upper portion of the penta prism 14. The casing has a top plate 27 which, when the casing is retracted in the chamber 16, defines the closed external appearance of the camera together with the penta housing 12.
The casing 20 is made up of a first chamber 21a and a second chamber 21b. A flash F is provided in the first chamber 21a, and an auxiliary light emitting device S is provided in the second chamber 21b. More specifically, a Fresnel lens 22 is provided on the front end of the first chamber 21a, and a xenon tube (light emitting element) 23 and a reflecting mirror 24 are arranged behind the Fresnel lens. The second chamber has a condenser lens 25 on its front end, and a striped pattern projecting unit 26 for generating a striped (dark and light) pattern behind the condenser lens 25. The condenser lens 25 is integral with the Fresnel lens 22.
The casing 20 is mounted in the chamber 16 of the camera body through a conventional pop-up mechanism such that it is movable between an extended or raised position and a retracted position.
Referring to FIGS. 7 and 8, right and left pop-up mechanisms are provided between the right and left side plates 28 of the casing 20 and the side walls of the chamber 16. Since the right and left pop-up mechanisms are equal in construction, only one of them will be described. The side plate 28 has two holes 28a and 28b into which shafts 34 and 40 are inserted. A first lever 32 and a second lever 38 are rotatably mounted on the shafts 34 and 40. The other ends of the levers are coupled through shafts 36 and 42 to the penta housing 12 in the chamber 16, thus forming a quadric crank chain pop-up mechanism for the casing 20. The first lever 32 is U-shaped, and is supported by the shaft 36 at the elbow. A torsion spring (not shown) is coupled to the shaft 42 of the second lever 38 to urge it counterclockwise in the figure; i.e. obliquely upward toward the extended position.
The shaft 42 is coupled to a locking lever 50, with which one end of the torsion spring mentioned above is engaged, so that the locking lever 50 is urged counterclockwise. The range of swing of the locking lever 50 is regulated; that is, the swinging of the locking lever 50 is stopped when a part of it strikes against the inner wall of the chamber 16. When the casing is retracted, the end of the locking lever 50 is engaged with the locking surface 32a of the first lever 32 to prevent the counterclockwise swing of the first lever. As a result, the movement of the casing 20 to the extended position by the torsion spring is prevented; that is, the casing is held in the retracted position.
The locking lever 50 is disengaged from the locking surface 32a by displacing it in a direction perpendicular to the drawing with a disengaging member (not shown) mounted on the side wall of the penta housing 12. Accordingly, when the casing 20 is moved to the extended position by means of the disengaging member, the flash F and the auxiliary light emitting device S are exposed simultaneously. Under this condition, the preparatory operations for light emission by the xenon tube 23 and for the projection of the striped pattern by the projecting unit 26 are accomplished.
When the photographer depresses the release button on the camera body 10, in the initial stage the striped pattern projecting unit 26 is electrically energized to generate a striped pattern. In the camera body 10, according to the contrast of the object with the striped pattern, the object's position is detected, and according to the position detection signal the lens is driven to a focused position. When the release button is further depressed the shutter is released; that is, the mirror is raised, the shutter curtain is run and the xenon tube 23 emits light.
If the striped pattern is oriented in a direction perpendicular to the optical axis of the camera, the range of distance in which the striped pattern image is clearly formed would be limited to a considerably small value. In view of this difficulty the present applicant has proposed, as described in U.S. Pat. No. 4,771,308, that, as shown in FIG. 5, a striped pattern A-B and a condenser lens 25 are so arranged that a prolongation of the striped pattern and a straight line which intersects the optical center of a condenser lens 25 and is perpendicular to the optical axis OS of the condenser lens meet at one point 01 on the optical axis OL of the camera lens L. With this arrangement, as shown in FIGS. 4A and 5, the striped pattern image is formed as a striped pattern a-b along the optical axis OL of the camera lens L. That is, the striped pattern a-b is clearly formed on objects lying along the optical axis OL, which allows an accurate and quick focusing operation.
Sometimes it is necessary to photograph a dark object without using the flash, and even if an object is light enough to render the flash unnecessary, its contrast may be low. In order to photograph such objects, it is necessary to use auxiliary light emitting means. It is unnecessary to use the flash unit, however, and therefore it is desirable that only the auxiliary light emitting device S be caused to emit light with the flash unit held retracted.
However, even if, in the above-described conventional structure, the front wall 16a of the chamber 16 is made of a transparent plate, the optical axis OS of the auxiliary light emitting device S is directed excessively downwardly in the retracted position, and therefore the image of the striped pattern A-B is formed as a striped pattern a1-b1 well below the optical axis OL of the camera lens (cf. FIG. 4B), which is so far away from the automatic focusing range that it is of no use.